1. Field of the Invention
The present invention relates to a connector type semiconductor package including cable connection interface ICs and optical semiconductor devices for optical interconnection and the like, and detachably connecting a signal connection connector such as an optical connector and the like.
2. Description of the Related Art
Recently, the number of personal information equipment have been rapidly increased and the demand for a great increase in the information communications capacity rises. Further, digital image information processing has been normally conducted. In this way, large amounts of data of information equipment and of communications equipment have been processed. Particularly in a server for receiving and transmitting information transmitted from terminal systems and a communication exchange system for constructing a network, the lack of processing capacity and of communications capacity has become a serious problem.
Only an improvement in LSI processing speed of, for example, a processor is not enough to process such high capacity information. It is necessary to conduct multi-processing such as parallel processing and distributed processing using many processor LSI circuits. Therefore, in many cases, lots of LSI circuits are combined and used in a single processing unit in a core information processing system or information exchange system. Additionally, in these systems, even a single architectural unit cannot be mounted on a single board and is frequently needed to be mounted on multiple boards or, in some cases, multiple racks. For that reason, wiring between boards and between racks becomes one of primary factors for determining processor capability. It is therefore important to secure the capacity of wiring members.
Normally, since interface circuits for wiring members between racks are mounted on boards, wiring between racks may be referred to as wiring between boards in a broader sense. The mounting technique at the time of wiring between boards is substantially significant. So is the performance of circuits and parts installed on board ends as well as transmission paths to be connected thereto.
Boards are mounted on a rack by connecting connector so as to enable maintenance, repairs and replacement in units of boards. A bookshelf mounting is a best known method for mounting. According to the method, mounting boards are mounted like a bookshelf on a back plane board which includes wiring members for bridging wiring members between boards and a board installation connector. Wiring outside the back plane board, i.e., wiring between racks is conducted using ribbon cables and coaxial cables through the connector.
The wiring members between boards transmit and receive signals which are processed on the boards without change if transmission speed is relatively slow and the distance is short. Meanwhile, if the distance is long, the speed is fast and wiring is laid out in a wide range, then the wiring members amplify and transmit signals and receive signals after processing them such as amplification or waveform shaping. The higher the signal frequency is, the more frequently the electrical signals are buried into noises and the bigger the transmission loss of connection paths becomes. It is necessary to prevent the signals from being buried into noises and to compensate the loss. For that reason, high speed, large capacity wiring members as mentioned above require interfaces for amplification and waveform shaping on board ends to ensure wiring between the boards.
Optical wiring characterized in that signal paths are non-inductive and that grounding is not necessary, is recently intended to be used for high speed wiring which is difficult to conduct by electrical wiring and for wiring in the environment surrounded by frequent electromagnetic noises. In this case, converting parts for converting an optical signal into an electrical signal is required. In addition, interfaces are required as in the case of the above-stated high speed electrical wiring.
Normally, interface circuits for electrical wiring between boards are ICs. They are mounted on the boards and input/output sections thereof are connected to a signal connection connector on board ends. In that case, however, mounting areas on the boards are reduced since areas for the interface circuits are necessary. Thus, additional boards are required. This results in an increase in wiring members between boards, an increase in the overall wiring length and therefore a decrease in system performance. To reduce the mounting area of the interface circuits and to reduce the number of parts, an active connector wherein interface ICs are installed in a signal connection connector has been developed and put to practical use.
In case of optical wiring, meanwhile, photoelectric transfer devices are always used whether interface ICs are installed or not. Due to this, optical semiconductor devices are usually mounted on a connector portion. In this case, too, it is advantageous that all semiconductor devices are installed into the connector portion to secure the mounting areas on the boards. Actually, optical wiring parts having interface circuits installed thereinto have been put to practical use.
FIG. 1 illustrate a connector portion having interface semiconductor devices installed thereinto, that is, a semiconductor package including a connector (which will be referred to as a "connector type semiconductor package" hereinafter). In FIG. 1, a connector insertion portion 3, a connector lock hole 4 and electrical terminals 11 for supplying electrical signals and power are provided in a package main body 1. Interface ICs and optical semiconductor devices are mounted inside the package main body 1.
In the package including interface circuits, the outline of electrical wiring can be made the same as that of optical wiring. Accordingly, description will be given to wiring hereinafter without particularly differentiating electrical and optical wiring.
The connector type semiconductor package shown in FIG. 1 is a so-called terminal insertion type package. That is, in the package, through holes for use as both insertion holes and as wiring terminals are provided in mounting boards to insert and mount parts into the boards. The mounting manner is similar to that of a DIP (Dual In-line Package) and advantageous to the connector type package since the mechanical alignment of part mounting positions on the board is possible and the mounting strength is large.
However, the insertion type package is disadvantage in that it requires through holes on the mounting substrate and that the signal terminal density cannot be very high. In other words, even if narrow print wiring pitches on the mounting boards are possible, it is necessary to widen wiring pitches on the connector portion. Compared with wiring density on a single board, the wiring density between boards become small. Owing to this, if a processor unit bridging a plurality of boards is to be constructed, widths of bus lines (or the number of signal lines and signal speeds) on the boards and those between boards become inconsistent. This possibly causes problems to system configuration.
To solve the problems, it is desired to realize a package capable of including many terminals to be connected on boards. The same thing is true of the board mounting of LSI circuits. That is why the package form of LSI circuits is changed with the times. There is proposed a surface mount type package wherein far more connection terminals can be provided than the conventional insertion package shown in FIG. 1.
The surface mount type package is characterized in that parts can be mounted only by providing installation patterns for, example, soldering on surfaces of boards as the name shows and that no through holes are required on the mounting boards. Therefore, in case of the surface mount type package, another circuits can be mounted on back surfaces of the boards, thereby making it possible to realize two-fold mounting density. Moreover, because of few constraints to mechanical density unlike through holes, the surface mount type package is capable of increasing terminal density so far as electrical characteristics, the package installation technique (soldering technique) and the like permit. This makes it possible to provide signal terminals of the same density as that of the wiring members on mounting boards. As a result, the wiring density on boards can be made same as that between boards.
As surface mount type LSI packages, SOP (Small Outline Package), QFP (Quad Flat Package), BGA (Ball Grid Array) can be cited. It is considered that they can be easily used as connector type semiconductor packages.
FIG. 2 illustrates a case where the surface mount type LSI package is applied to a connector type semiconductor package. FIG. 2 represents the work of the inventors of the present invention and is disclosed in this section to explain the background of the invention, and is not an admission that FIG. 2 represents prior art. As shown in FIG. 2, a package main body 1 is provided with signal connection terminals 2. A connector lock key 13 is provided on one end of a cable connector 12 from which the cable connector 12 is inserted into the package main body 1. A signal wiring cable 14 is provided on the other end of the cable connector 12. This exemplifies the above-stated QFP type package. The terminals 2 are fixedly soldered to print wiring members independently of one another, thereby realizing high density terminal connection.
It is simplest to provide the same number of the wiring members in the cable 14 as that of the terminals connected to the connector type package. However, if a signal multiplexing circuit is incorporated into an interface circuit, the number of wiring members within the cable which are actually connected to the package can be reduced. The method is particularly easy to use for optical wiring and is advantageous to the realization of smaller space and lighter weight of the wiring cable while maintaining the same wiring capacity as that on boards.
As described above, the connector type semiconductor package is effective means for wiring interface parts such as wiring between boards. Nonetheless, the above-stated conventional connector type semiconductor package has the following problems.
The surface mount type LSI package is normally arranged line-symmetrically (SOP) or point-symmetrically (QFP, BGA) about the center of the package. The reason is the adoption of a method for pressing the package against boards during mounting and for collecting slightly uneven shapes of respective connection terminals by deforming the terminals (leads or balls) altogether so as to ensure that all of the many narrow pitch connection terminals can be soldered to the mounting boards, respectively in a uniform manner.
Accordingly, if simply using the surface mount type LSI package as shown in FIG. 2 as a connector type semiconductor package, then terminal arrangement symmetry is thrown into disorder and problems typical of the surface mount type LSI package occur. That is, the package is inclined toward the connector side by the application of pressure onto the package during mounting and soldering defects tend to occur to connection terminals on the surface facing the connector surface. Furthermore, the QFP type connection terminals shown in FIG. 2 have lead terminals only in three directions which should be four directions. The package tends to be pressed and shifted (pressure shift) by a group of connection terminals arranged on the surface facing the connector after the application of pressure onto the package during board mounting.
The surface mount type package is fixed to surfaces of the mounting boards only by soldered joint, as the name tells. Therefore, the fixing strength larger than connector disconnect force is not necessarily secured even if auxiliary adhesive is used sometimes. Even though the package fixing strength larger than the connector disconnect force is ensured, stress is given to the connection terminals as a result of connector disconnect and tension generated by providing the connection cable. This lead to an increase in connection deteriorating phenomena such as a solder creep. In other words, the connection reliability of connection terminals might be badly affected, reliability of parts and mounting might be deteriorated and thus the system reliability might be considerably lowered.